Laser programmable redundancy and yield improvement in a 64K DRAM

Yield improvement obtained with laser programmed redundancy in a 64K DRAM has range from 3000 percent during early model making to 500-800 percent after two years of volume production. The electrical design constraints on 64K redundancy organization are reviewed. The explosion and wicking phenomenon of polysilicon links by ~50 ns, 1.064-μm wavelength laser pulses is discussed in relation to the target geometry, laser spot size and targeting accuracy. The system hardware and main software modules are detailed. In particular, the algorithms for testing, repair diagnosis, and target coordinate calculation are explained. Elemental time analysis of the main operational steps is reviewed and emphasis on strategy for main operational steps is reviewed with emphasis on strategy for improved throughput. Evolution of the laser programming technology to the next generation of VLSI devices involves smaller spot sizes and submicrometer positioning accuracy.